Due to various sociological and technicological changes in present day society, the types of food which the public ingests as well as the manner in which these foods are prepared has been drastically altered in the last several years. So-called "fast-food" restaurants have proliferated in recent times to such an extent that the percentage of people who frequent these establishments on a regular basis has increased greatly. Among the reasons for this increase, is the technology which has recently been developed for quickly heating and preparing the foods. One of these advances has been the microwave oven which greatly shortens the time it takes to initially heat or reheat the food.
However, many disadvantages abound which render these types of establishments unpalatable. For example, while the microwave oven would adequately heat the food which is placed therein, the typical platter or food receptacle which is placed under the food while it is being heated in the microwave oven does not become warm or retain any heat. Additionally, if the food is placed within a so-called disposable container containing thermal insulative material, the food contained therein will cool relatively rapidly and not retain heat for an appreciable amount of time. This situation also is true when food is prepared at a central kitchen to be dispensed to individuals not in proximity with the central kitchen, such as food in hospitals, nursing homes and the like.
Much time and effort has been undertaken to develop a heat-retaining food container which would ensure that food placed therein would retain its heat for a relatively long period of time. U.S. Pat. No. 3,557,774 issued to Kreis, U.S. Pat. No. 3,734,077 issued to Murdough et al, U.S. Pat. No. 3,837,330 issued to lanigan et al and U.S. Pat. No. 3,916,872 issued to Kreis et al and U.S. Pat. No. 4,246,884 issued to Vandas are all directed to heat-storage dishes which are heated with or without food provided therein to maintain the food at a proper temperature for a substantial period of time.
U.S. Pat. No. 3,837,330 describes a heat-retaining server which is preheated to a particular temperature prior to the placement of food thereon. The server contains a heat-retention member formed of aluminum, an aluminum alloy, or some other rigid material having superior heat absorbing and retaining properties. An upper metal shell and a lower metal shell surround the heat retention member.
U.S. Pat. No. 3,557,775 shows a heat storage dish provided with a heat insulating filler such as rockwool provided between two walls composed of non-corrosive chromium nickel sheet steel. Additionally, a heat-storage plate consisting of aluminum is also employed.
U.S. Pat. No. 3,734,077 discusses a heat-retaining food server employing a heat-retaining pellet formed of the same material discussed with respect to U.S. Pat. No. 3,837,330. A resilient pad, formed of non-woven glass fibers or any other suitable insulating and cushioning material, occupies the space between the undersurface of the pellet and a lower shell. An upper shell is included and, along with the lower shell, are formed from stainless steel or any other material having similar properties of durability and strength.
U.S. Pat. No. 3,916,872 depicts a heat-storage plate provided with an insulation member formed of a plastic-type material having sufficiently low thermal conductivity and a heat storage plate composed of a substantially circular metallic body member.
U.S. Pat. No. 4,246,884 shows a plate warmer containing a heat storage material comprising beads of synthetic petroleum wax which are compressed to form a solid core. This core is surrounded by a top shell member fabricated from a sheet of stainless steel.
All of the heat-retaining food servers listed hereinabove utilize a heat storage or insulation means provided adjacent to or surrounded by a metallic plate or shell. Consequently, none of the food containers disclosed in these patents could be utilized in a microwave oven.
U.S. Pat. Nos. 4,183,435 and 4,327,136 issued to Thompson et al as well as U.S. Pat. No. 4,217,476 issued to Bellavoine illustrate containers for food products to be cooked or reheated in microwave ovens. While the patent to Bellavoine does indicate that polystyrene foam is provided within a meal tray to insure thermal insulation between various compartments in the tray, none of these references utilize a heat-retentive medium therein.